A polymer containing a phosphorylcholine group has a structure similar to that of a phospholipid constituting a cell membrane, and therefore has high biocompatibility, to exhibit superior properties as a medical high molecular material, such as non-activating ability of a complement including blood coagulation factor, lack of biomaterial (including protein and cells) absorbing property, antithrombus property, moisture holding property, and lipid bilayer stabilizing ability (Kazuhiko Ishihara, et.al., Journal of Biomedical Materials Research, 24(1990) 1069-1077, Kazuhiko Ishihara, et.al., Journal of Biomedical Materials Research, 25(1991) 1397-1407).
Development of bio-related materials utilizing these properties has actively been performed. For example, it is described in Japanese Laid-open Patent Application No.91-39309 that a copolymer of 2-methacryloyloxyethylphosphorylcholine and an ester of methacrylic acid is a superior biocompatible material. It is described in WO93/01221 that, when a polymer containing a phosphorylcholine group is utilized as a coating material, the coated article can be used as a material having a biocompatible surface for various bio-related purposes. It is disclosed in WO93/16117 that a water-soluble cellulose derivative produced by graft polymerization of a water-soluble cellulose with 2-methacryloyloxyethylphosphorylcholine has both biocompatibility and affinity with cellulose, and can be used as biocompatible material for, e.g., hemocatharsis. It is disclosed in Japanese Laid-open Patent Application No.84-43342 that a high molecular composition of a moisture sensor material consisting of a polymer having a phosphorylcholine group and a thin film material which is a water-soluble polymer is useful as a moisture sensor material. It is disclosed in Japanese Laid-open PCT application No. 95-504459 that a high molecular composition of a polymer having a phosphorylcholine group and a polymer having desirable mechanical and/or physical properties is suitable for a biomedical material. Various monomers, homopolymers, and copolymers having a phosphorylcholine group, and methods for producing the same are previously known as described in, e.g., Japanese Laid-open Patent Application Nos. 79-63025, 83-154591, 88-222183, 93-107511 and 94-41157, and WO093/01221.
Although a polymer or copolymer having the phosphorylcholine group has significant biocompatibility, mechanical properties such as dynamic strength and durability are not always sufficient, in terms of a medical material. Thus, various studies have been made regarding copolymerizable monomers to be copolymerized with the monomer having a phosphorylcholine group. An attempt to improve dynamic strength and durability by mixing a hydrophobic polymer having such properties has also been made. However, in the case of the polymer having a phosphorylcholine group, which is a functional group exhibiting a uniquely significant water-solubility, sufficiently good result has not yet been obtained unlike the case of conventionally performed mixing of hydrophobic polymers with another hydrophobic polymer.
Alternatively, it is known that a segmented polyurethane is superior in dynamic properties, and has better blood compatibility than other materials (Japanese Laid-open Patent Application No.82-139352, European Patent Specification No.68385, U.S. Pat. No. 4,379,904, WO83/00695). Such segmented polyurethanes are widely used as medical materials such as blood circuits, artificial hearts, various catheters, and medical sensors ("Artificial Organs" Ed. Tetsuzo Agishi, 1994-95, Published by Nakayama Shoten). However, when these materials are used for a long time in an organism, inflammatory response, deterioration of materials caused by cell adhesion, and calcification occur. Therefore ideal antithrombus property is not always obtained, thus not being sufficient.
An attempt to mix two or more sorts of high molecular compounds having different properties to reform the material is called "polymer blend" and is commonly performed. When a film is produced with a mixture of two high molecular compounds having properties in contrast, such as a mixture of a high molecular compound having high hydrophilicity and a high molecular compound having high hydrophobicity, or a mixture of a high molecular compound having a high crysterization property and a high molecular compound having a high non-crysterization property, molecules of high molecular compounds having the same property gather by movement of molecules, to occur phase separation. Reform of materials utilizing the phase separation is also a common method of polymer blend. A multi-phase structure material has been developed utilizing phase separation mechanism of a high molecular mixture system which can be mutually dissolved. However, if high molecular compounds having extremely different hydrophilicity or hydrophobicity are mixed, aggregation or cloudness occurs because of phase separation, thus being not suitable for a biocompatible material for preventing adhesion of cells of the order of micrometers.
For example, in the method for producing a high molecular compound described in the aforementioned Japanese Laid-open PCT Application No.95-504459, 1:2 copolymer of 2-(methacryloyl)oxy-2'-(trimethylammonium)ethyl phosphate and n-dodecyl methacrylate, and segmented polyurethane are dissolved in a single solvent of dichloromethane or a mixed solvent of ethyl acetate and propane-2-ol. However, when the solvents are employed with such combination of high molecular compounds, only a part thereof is dissolved or swelled, and a uniform solution cannot thus be obtained. Therefore, a film obtained by evaporation of the solvent from such an ununiform solution cannot be utilized as a biocompatible material because of aggregation and cloudiness. In the combination of high molecular compounds having extremely different hydrophilicity or hydrophobicity, it is known that a mixture system without cloudiness in macro observation can be obtained as long as the compounds are covalently bonded to form a blocked copolymer. However, such a mixture is not known produced by mere mixing of two high molecular compounds.